In a stacked battery in which a plurality of power generating elements is stacked, it is desirable to detect internal resistance as accurate as possible. For example, in a fuel-cell, wettability of an electrolyte membrane can be determined by understanding internal resistance. High internal resistance is associated with low wettability of an electrolyte membrane with a tendency to dry out. Low internal resistance is associated with high wettability of an electrolyte membrane. Operating efficiency of the fuel-cell is variable depending on wettability of an electrolyte membrane. Therefore, an optimal wet state of an electrolyte membrane can be constantly maintained by controlling operation in accordance with wettability of the electrolyte membrane as estimated based on internal resistance.
A device for measuring internal resistance of a fuel-cell is disclosed in JP-2009-109375-A.